Device and method for side-impact identification

ABSTRACT

A device and a method, respectively, are proposed to detect side collisions, in which a temperature sensor is located in a motor-vehicle side section. In case of a side collision, the temperature sensor measures the short-term adiabatic temperature increase and a control device detects a side collision as a function of the measured temperature increase and the temperature gradient. A triggering decision is made by plausibility testing using an acceleration sensor.

BACKGROUND INFORMATION

[0001] The present invention is based on a device and a method fordetecting side collisions according to the species defined in theindependent claims.

[0002] A device for detecting side collisions is known from the EuropeanPatent EP-667 822, in which a pressure sensor is located in a sidesection of a vehicle body. When a side collision occurs, the adiabaticpressure increase in the side section is evaluated for side-collisiondetection. The side section is substantially closed in this case.Adiabatic means that the amount of heat remains constant.

SUMMARY OF THE INVENTION

[0003] The device and the method according to the present invention fordetecting side collisions having the features of the independent claimshave the advantage over the related art that a temperature sensorlocated in the side section of the vehicle body is less complicated thana pressure sensor. This results in cost savings. Also, no filtering ofnoise signals, such as acoustic frequencies, is required. Furthermore,the device according to the present invention and the method of thepresent invention are robust and react to actual deformations of thevehicle body. Thus, the method and the device according to the presentinvention are less sensitive with respect to events (driving throughpotholes, driving over the curb or slamming of the door) that suggest aside collision, but are not supposed to trigger a restraint system.

[0004] By the measures and further refinements mentioned in thedependent claims advantageous improvements of the device and the methodfor side-collision detection according to the present invention are madepossible.

[0005] It is particularly advantageous that the temperature sensor isdesigned as a micromechanical sensor, so that the temperature sensor iseasy to manufacture in mass production. The micromechanical sensor couldbe an extremely precise temperature sensor.

[0006] By designing a housing around the temperature sensor in the sidesection of the vehicle it is protected against radiation, and theadiabatic effect is increased since the air surrounding the temperaturesensor is better insulated.

[0007] Using an acceleration sensor also has the advantage that aplausibility signal is generated, which is used to check a triggeringsignal obtained as a result of the temperature-sensor measurement. Inthis way, undesired triggering decisions for a restraining device andunnecessary injuries are prevented and costs are saved for the user of arestraint system. As an alternative, it is also possible that theacceleration sensor makes the triggering decision, and the temperaturesensor generates the plausibility signal.

[0008] Furthermore, it is advantageous that the restraint devices areonly triggered if the absolute temperature change and a temperaturegradient exceed specified threshold values. It is ascertained especiallywith the temperature gradient that the temperature increase isshort-term, so that a warming as a result of the vehicle being exposedto sunlight does not lead to an undesired triggering.

[0009] Finally, it is also advantageous, on the one hand, thatredundancy is obtained by arranging a plurality of temperature sensorsin a side section of a vehicle and, on the other hand, a temperaturesensor will in each case be located near a deformation location of theside section.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Exemplary embodiments of the present invention are shown in thedrawings and are explained in detail in the following description.

[0011] The Figures show:

[0012]FIG. 1 a side section with a temperature sensor;

[0013]FIG. 2 a block diagram of the device according to the presentinvention;

[0014]FIG. 3 a diagram comparing the temperature change with therelative volume change;

[0015]FIG. 4 a micromechanical temperature sensor in side view;

[0016]FIG. 5 a top view of the micromechanical temperature sensor;

[0017]FIG. 6 the micromechanical temperature sensor in a housing; and

[0018]FIG. 7 a flow chart of the method according to the presentinvention.

DESCRIPTION

[0019] Restraining systems, such as airbags, find increasing use inmotor vehicles. Primarily, it is important in this context to rapidlydetect an accident so that restraining means such as airbags and belttighteners may be used efficiently. However, it is equally important toprevent an undesired triggering of restraining devices. Especially in aside collision the reaction time for the side-collision sensor systemand the control system of the restraint systems is considerably shorterthan in a head-on collision. A side collision in a side section of thepassenger compartment should be detected early by the beginningdeformation of the side section. Since side sections often constitute asubstantially closed body, i.e., a cavity, an adiabatic pressureincrease results in response to a deformation of the side section, whichis accompanied by an adiabatic, rapid temperature increase. According tothe present invention, at least one correspondingly fast temperaturesensor is located in a side section of a vehicle, to detect sidecollisions. The collision force and/or the collision speed areascertained by evaluating the absolute temperature increase and thetemperature gradient, and the assurance is obtained that an adiabatictemperature increase is involved. The impact force and/or the impactspeed may be determined based on the degree of deformation of the sidesection within a specified period of time. Combining the temperaturesensor with an acceleration sensor allows a plausibility check of thetemperature sensor's side-collision signal. Thus, it is ascertainedwhether an actual side collision is involved and not a temperatureincrease caused, for instance, by a welding torch.

[0020] The fast temperature sensor may be advantageously designed as amicromechanical temperature sensor. Micromechanics make a temperaturesensor possible that is capable of very precise temperaturemeasurements, and a micromechanical sensor is easy to produce in massproduction.

[0021]FIG. 1 shows a side section 1 of a vehicle in which a temperaturesensor 2 is located. Side section 1, here a vehicle door, hastemperature sensor 2 in a cavity of the side door, depicted here as afunctional block. Not shown is the evaluating electronic system, whichmay either be arranged in side door 1 together with temperature sensor 2or may be arranged externally at some other location in the motorvehicle. A measurement amplifier, for instance, may be integrated on thechip with the temperature sensor, while digitization is carried out in acontrol device.

[0022]FIG. 2 shows a block diagram of the device according to thepresent invention. Temperature sensor 2 is connected to an input of asignal-processing unit 3. A data output of signal processing unit 3leads to a vehicle bus 4 to which a control device 5 is connected.Control device 5 is connected to restraint means 6 via a datainput/output. Component parts of the electronic system, i.e., themeasurement-value amplifier and the analog-digital converter, may bearranged in alternative fashion as described above.

[0023] Temperature sensor 2 generates electrical signals correspondingto the temperature, which are amplified and digitized bysignal-processing unit 3. These digital data are then transmitted viabus 4 to control device 5, which processes the digital data in such away that the absolute temperature increase is compared to a specifiedthreshold value and the temperature gradient is also compared. Thetemperature gradient indicates the temperature change per time. In thismanner it is ascertainable whether an adiabatic air-pressure increase isinvolved or not. In an adiabatic process, the temperature increase mustoccur within a very brief period of time. If the absolute temperatureincrease and also the temperature gradient exceed specified thresholdvalues, which were experimentally determined, a triggering signal willbe generated that will be checked with a measuring signal of anacceleration sensor, if necessary. The measuring signal of theacceleration sensor indicates whether a side collision could indeed beinvolved or not. Thus, a plausibility check is carried out. If even thismeasuring signal is above a specified enabling threshold, the triggeringdecision is accepted and restraint means 6 are triggered. Airbags andbelt tighteners are such restraint means 6.

[0024]FIG. 3 shows a diagram which relates the temperature change in aside section of a vehicle implemented as a cavity to the relative volumechange. For instance, in case of a volume change of approx. 10%, atemperature increase of 13 Kelvin will already be obtained. This ensuresthat a side collision is already detected at an early deformation and atriggering decision may be generated. Since the door is not perfectlysealed, air escapes from the door during and after the side collision,so that soon after deformation the pressure and temperature will havereached approximately the values that prevailed before the sidecollision. This means that a lower degree of sealing of the door willresult in decreased sensitivity of the side-collision detectionaccording to the present invention. A relationship exists between theair temperature prior to the event, temperature T₀, the temperatureincrease ΔT and the volume change ΔV. In the leading area for smalltimes (in the milli-second range), the pressure loss after the sidecollision due to door permeability is negligent, and the followingresult will be achieved for the adiabatic state change with the aid ofmeasured temperature T₀+,${\Delta \quad {T:\quad {\Delta \quad T}}} = {T_{0}\left( {\left( \frac{V_{0} - {\Delta \quad V}}{V_{0}} \right)^{1 - Κ} - 1} \right)}$

[0025] with K being the adiabatic exponent of the air and V₀ the doorvolume. From this, temperature change ΔT may be estimated, an ambienttemperature of T₀=293 Kelvin and a decrease in the door volume of 10%resulting in a temperature increase of approximately 13 Kelvin.

[0026]FIG. 4 shows a side view of a micromechanical temperature sensor,which is arranged in a side section of the motor vehicle according tothe present invention. A temperature sensor 7 made of platinum isimplemented on a membrane 8 having poor thermal conductivity. Membrane8, in turn, is arranged on a silicon frame 9 produced by means ofmicrostructuring. Membrane 8, in this case, is made either of silicondioxide or of silicon nitride, which are known dielectrics insemiconductor technology. These dielectrics have poor electricconductivity and thus also poor thermal conductivity. As an alternative,other dielectrics may be used.

[0027] Temperature sensor 7 is implemented as a platinum thin-layerelement and has a temperature-dependent resistor. Thus, the temperatureon membrane 8 may be inferred by measuring the resistance of theplatinum element. Since the thermal capacity of membrane 8 is very lowdue to minimal thickness and low mass, membrane 8 very quickly assumesthe temperature of the ambient air. Due to its low thermal conductivity,membrane 8 is thermally decoupled from the silicon frame and the bodyshell connected thereto, so that a temperature increase of the platinumelement may occur without the thermally inert body shell, which has alarge mass with a large heat capacity, having to be heated also.

[0028]FIG. 5 shows a top view of the micromechanical temperature sensor.Membrane 8 is located on silicon frame 9. Platinum sensor 7 hasconductors 10 (printed circuit traces) leading to so-called bond pads towhich the terminal wires, which provide the connection to otherelectrical or electronic components, must be soldered or bonded.

[0029] In FIG. 6, micromechanical temperature 13 shown in FIGS. 4 and 5is accommodated in a housing. The housing includes a housing base 15 towhich temperature sensor 13 is attached, and a housing top 12 having anopening 14 through which a pressure change in the ambient air istransmitted. If an adiabatic process is involved, this pressure changeis accompanied by a temperature change.

[0030] In FIG. 7, the method according to the present invention isrepresented as a flow chart. In method step 16, a temperature signalfrom temperature sensor 2 is amplified by signal processor 3 anddigitized and transmitted to control device 5. In method step 17,control device 5 calculates the absolute temperature increase and thetemperature gradient. In method step 18, the absolute temperatureincrease and the temperature gradient are compared to predefinedthreshold values to ascertain whether a side collision has occurred ornot. If both threshold values are exceeded, a side collision is present,and this detected side collision is checked in method step 19 usingsignals from an acceleration sensor. If the signal from an accelerationsensor is also above an enabling threshold, i.e., the acceleration inthe lateral direction of a vehicle, it will then be determined in methodstep 20 that it exceeds an enabling threshold, and a triggering decisionwill be transmitted to restraint means 6 in method step 21.

[0031] If it was determined in method step 18 that either the absolutetemperature increase or the temperature gradient is below theindividually specified threshold value, a return to method step 16 isimplemented, and the instantaneous temperature value is checked. If itwas detected in method step 20 that the signal of the accelerationsensor is below the specified enabling threshold, a return to methodstep 16 is also implemented to call up the ambient-temperature signal.

[0032] Rapid information regarding the thus occurring temperatureincrease ΔT may also be obtained by a slower temperature sensor, bymeasuring the temperature gradient. In the first 20 ms after deformationbegins, the temperature increase occurs according to an exponentialfunction:

[0033] T(t)=ΔT(1−e^(−t/τ))

[0034] τ is the thermal time constant of the air-temperature change inthe vehicle cavity. It is experimentally determined and is assumed to beconstant over the temperature and service life.

[0035] If this temperature is measured, for instance, after 0.5 ms andafter 2 ms, the following is obtained:

[0036] T(0.5 ms)=ΔT(1−e^(−0.5 ms/τ)), and

[0037] T(2 ms)=ΔT(1−e^(−2 ms/τ)), respectively, and thus

[0038] ΔT=(T(2 ms)−T(0.5 ms)):(e^(−0.5 ms/τ)−e^(−2 ms/τ)).

[0039] The relatively slow temperature sensor assumes temperatureincrease ΔT, for example, only after 50 ms, that is, much too late.Nevertheless, with the aid of this “trick”, information regarding theoccurring ΔT is obtained already after 2 ms and then compared to aspecified threshold value to detect a side collision.

[0040] An alternative method is to evaluate the first derivative of thetemperature variation. The actual temperature increase must be seen as ajump function, which is made of a thermal substitute circuit diagram ofthe temperature sensor, made of a thermal resistor r and a thermalcapacitance. The temperature is tapped off by way of the thermalcapacitance. A differential equation results from the analog voltagecycle and the current equation, the differential equation simulating thejump function by a sum of the weighted first time derivative of thetemperature variation and the temperature variation per se. Theweighting results from the values for the thermal resistance and thethermal capacitance, which depend on the technological properties of thetemperature sensor. Using a slow sensor, information regarding thetemperature rise may already be available after a few ms. In a furtherrefinement it is provided that only the first time derivative of thetemperature variation is used to predict the temperature rise.

What is claimed is:
 1. A device for detecting side collisions in thecase of a vehicle, the device comprising at least one sensor (2) in avehicle-body side section (1) that is implemented as a cavity, the atleast one sensor (2) being connectable to a control device (5), whereinthe at least one sensor (2) is in the form of a temperature sensor andthe control device (5) uses a temperature increase to detect a sidecollision, which the at least one temperature sensor (2) measures in theside section (1).
 2. The device as recited in claim 1, wherein the atleast one temperature sensor (2) is in the form of a micromechanicaltemperature sensor (13).
 3. The device as recited in claim 1 or 2,wherein the at least one temperature sensor (2) is accommodated in ahousing (12, 15) in the side section (1).
 4. The device as recited inone of the preceding claims, wherein the device has at least oneacceleration sensor, which is connectable to the control device (5). 5.The device as recited in one of the preceding claims, wherein thecontrol device (5) has means for triggering restraint means (6) inresponse to a side collision, the control device (5) in each casecomparing the absolute temperature change and/or a time derivative ofthe temperature rise in the side section (1) with at least one specifiedthreshold value and making a triggering decision as a function of atleast one of these comparisons.
 6. The device as recited in claim 4 or5, wherein the control device (5) compares a signal from the at leastone acceleration sensor with an enabling threshold and gives thetriggering decision if the signal exceeds the enabling threshold.
 7. Thedevice as recited in one of the preceding claims, wherein the device ina side section (1) includes a plurality of temperature sensors, whichmay be placed in different locations of the side section (1) designed asa cavity.
 8. A sensor for detecting side collisions, which is located ina motor-vehicle side section (1) designed as a cavity, wherein thesensor is in the form of a temperature sensor.
 9. A method for detectingside collisions in the case of a vehicle, in which signals from a sensor(2) in a vehicle-body side section (1) designed as a cavity are used todetect side collisions, wherein a temperature sensor (2) generatessignals in the side section (1), and a side collision is detected whenthe temperature sensor (2) measures a temperature increase.
 10. Themethod as recited in claim 9, wherein, given a side collision, theabsolute temperature change, and/or the temperature gradient of thetemperature increase, in each case is compared to at least one thresholdvalue, and a triggering decision is made as a function of at least oneof these comparisons.
 11. The method as recited in claim 10, wherein asignal from an acceleration sensor is compared to an enabling thresholdand the triggering decision is enabled if the signal exceeds theenabling threshold.
 12. A control device for implementing the method asrecited in one of the claims 9 through 11, wherein the control device(5) is connectable to a temperature sensor (2).